ThompsonTransducerTheoryLoudspeakerDesignFA4740KrisThompson

ThompsonFunctionalGoals

ThespeakersIintendtobuildwillbeusedasstudio/mixingmonitors.TheywillbethemainformofplaybackformycomputerwhereIdomostifnotallofmysongandsoundcreation.Sincetheyaremixingmonitors,theywillneedtoaccuratelyreproducetheentirespectrumofhumanhearingascloselyaspossibleandwithaslittledistortionorcolorationaspossible.Also,sincemosthomelisteninghappensaroundthe75dBto85dBrange,myspeakerswillbeabletoproducesoundofhighqualityinthatrangeaswellaslouderifneeded.1 GiventhatImnotsurewherethesespeakersaregoingtoliveIamgoingtobuildthecabinetstobestreproducesoundsinafunctionallysizedbox.Theywillnotbesmallbookshelfspeakersnorwilltheybeleviathansthatstand6feettallliketheWilsonAudioSpecialtiesMAXXSeries2.TheywillberoughlythesamesizeastheCM7sin212,whichshouldallowampleroomforthewoofersandtweeter.2ThesubwooferwillbemadeinthesamewayastheThunderactivesubwoofermadebyNorthCreek.3ThisisbyfarthebestsoundingsubIveheardandIvealwayslikedsoIdecidedtomakeonemyself. Beingstudiogrademonitors,theywillbeabletorecreatetheentirespectrumasaccuratelyaspossible.Withthesubwoofertheyspeakerswillbeable1LoudspeakersPg.2502http://www.northcreekmusic.com/CM7/CM7TowerCabinet.PDF3http://www.northcreekmusic.com/Thunder/ThunderInfo.htm

Thompsontogetdownto20Hz.Thewooferswilltakeoverfrom100200Hzupto1000Hz.Thetweeterswillcoverfrom1000Hzup.Allthefrequenciesillbecoverasflataspossibleduetomydriverselection Whilethespeakersreachcrisp,clearsoundsIalsowantthemtolookgood.Thecabinetswillbeproperlyconstructedandwillbeaclosedboxtypeforthewoofer/tweetercabinetandalsoasealedboxforthesub.TheMDFwillbefinishedwithblackglosspaintaclearcoatenamelforprotection. Thesespeakerswillproducehighqualitysoundfromeachdriverthatissensitiveat90dB.Thesubwooferissensitiveat90dB4,thewoofersat88dB5andthetweeterat95dB.6Duetothetweetershighersensitivityitwillhavetobeattenuatedtomatchtheothertwomoreclosely.TechnicalGoals

ThesespeakerswillbeabletopumpouthighSPLlevelsbutnotridiculouslyhigh.Withthesensitivitiesofallthedriversbeingnear90dBmyspeakerswillproducethatSPLataonemeterrange,whichiswhereIwantmyspeakersbespatiallycomparedtomewhenImixormakesongs.Thiswillbedoneby4http://www.madisound.com/catalog/PDF/peerless/830844.pdf5http://www.madisound.com/catalog/PDF/seas/P18RNX_PH135008.pdf6http://www.madisound.com/catalog/PDF/neocd3.pdf

Thompsonattenuatingthetweeterdownto90dBandkeepingtheotherdriverswheretheyare. IntheendlesssearchofdriversIlookedatinthisprojectIcameoutwithonlyneedingtomakeathreewaysystemtoaccomplishwhatIwanted.Iwantedtogetasubwooferthatcouldgoallthewaydownto20Hzprettyeasilyandwastoldthatthesubwooferin212hadaPeerlessXLS12subwooferwithapassiveradiator.7SincethisisthesubwooferIwantedtobasemyownsubwooferoffofIchosetogowiththesamesetupneverlookedback.TheXLSIoriginallypickedhadafrequencyresponsenear20HzthatwasabitjaggedandIthenlookedattheXXLSsubandithadamuchbetterresponseinthatrangesoIwentwiththeXXLSovertheXLS.897http://www.northcreekmusic.com/Thunder/ThunderInfo.htm8http://www.madisound.com/catalog/PDF/peerless/830844.pdf9http://www.madisound.com/catalog/PDF/peerless/830500.pdf

ThompsonPeerlessXLS

PeerlessXXLS

Formywoofer/midrangedriverIwasinterestedinfindingadriverthatcouldgetprettylowbyitselfandstillgohighintothefrequencyrangewhile

Thompsonkeepingaflatresponsewithlittledistortion.IlookedonmadisoundandotherwebsitesbutdidntfindanythingparticularlyinterestinguntilIwenttozaphaudio.Heretheyhadalistofdriversandpeerreviewsonthem.Theyrateddriversontheirsounds,usability,andconsistency.ItwasherethatIfellfortheSEASPrestigeP18RNXP7PolyConeWoofer.Ithasalargemagnetforgoodtransientresponseaswellaslongcoppercladaluminumvoicecoilthatcantravelfarandhaslittledistortion.Thedesignaroundthespideralsoreducesniceescapingfrombehindthecone.Ontopofallthatthedrivercangofrom40Hzupto2500Hz,whichwaswhatIwaslookingfor.Thefrequencyresponsecurveisalsoreallyflatupto1000Hzandgetabitwobblyafterbutnotbyreducingoutputbutincreasingit.10

SEASPrestige7PolyConeWoofer

10http://www.madisound.com/catalog/PDF/seas/P18RNX_PH135008.pdf

Thompson Mysearchfortweeterwasssimpleone.Iwaslookingforaniceflatresponsefromarelativelylowfrequencyforatweeter.IfirstlookedattheHiViRT1CAIsodynamicRibbontweeterandlikedwhatIsaw.11Theresponsecurvelookedverynicefrom1000HzandupbutIcontinuedlookingandcameacrosstheFountekNeoCD3.0Ribbontweeteranditsresponseblewtheotheroneoutofthewater.12Thistweeterwasflatfrom1000Hzallthewayupto40,000HzandIrealizedthiswasthetweeterIwanted.ItwillhavetobeprotectedfrommyactivedigitalcrossoverlikeJohnhadtodowithhistweeter,butitwillmakemyspeakerssoundamazing.

11http://www.madisound.com/catalog/PDF/hivi/rt1ca.pdf12http://www.madisound.com/catalog/PDF/neocd3.pdf

Thompson FormycrossoversIwasntsurewheretostart.Thewholeideaveryconfusingonceyoustarttogetintotheliteratureonit.AftersiftingthroughpagesandpagesonitIdecidedonanthreewayactivedigitalcrossovernetwork.ThisbeingthefirsttimeIameverdealingwithbuildingacrossoverthetaskwasdaunting.Ireadaboutthemandactivehadalltheperksoverpassiveduethepossibilitiesthatactivegivesyou,nottomentionthelongevity.13Anactivesystemallowyoutopowereachsetofspeakersonitsownampwhichpromotesflexabilityaswellasgivesyoutheoptiontochangesettingsonthefly.Itookitonestepfurtherandwentforadigitalcrossoverthatwill:a)allowmetochangedelayandfiltersettingsdependingontheroomIendupinandb)keepthehumanelementoferroroutofmydesign.IvechosenthesamecrossoverasJohndidduetoitsfunctionalityandprice.IwillbeusingtheBehringerUltradriveProDCX2496. MycrossoverpointswillbebasedonthefigurebelowfromIntroductiontoLoudspeakerDesign.Itshowsthesuggestedcrossoverpointsfordriversdependentontheirdiameter.Mysubwooferwillbea12driversomycrossovershouldbebelow863Hz.Thisisfartohightogofromstereotomonosound.Iwillcrossoverat100Hztoallowforthebasstoseemtocomefromthemainleftandrightspeakers.Thecrossoverbetweenmy7SEASdriverandmytweetershouldbenohigherthan13LoudspeakerCookbookPg167

Thompson1730Hz.14Iwillcrossoverat1500Hztoallowadequateroomforboththetweeterandwoofertosumandtakeadvantageoftheniceresponsesfrombothdriversatthatfrequency.

MyamplifierswillbeanAlesisRA150topowerthetweeter.Thisamphas50Wofpowerinstereo,whichprovidesheadroomovermy17Wnominaltweeters.ACrown602willdrivethe7woofersinstereomode.Thisampprovides300WachannelandmywooferhaveashorttermRMSof250Wandanominalof80W,providingatonofheadroom.ThesubwooferisdrivenbyaCrown402,whichissettobridgedmono.Sincethesubneedstobepowerful,theampwillprovideawhopping900Winbridgedmono,whichismorethanenoughtodrivethesubat100Wnominal.

FormycabinetdesignIoriginallywantedtobuildacasesimilartocaseLintheimagebelow.15Thisdesignofferstheflattestresponseacrossthespectrumbut14IntrotoLoudspeakerDesignPg109

Thompsonisalsodifficulttobuild.Imnotproficientinmywoodworkingskillsandamnotwillingtomakeacasewithcompactangleswrongandhavethesoundsufferintheprocess.IwillinsteadfollowthecaseinstructionsfortheThundersubasitisdisplayed.ThecaseisthetypeoflookIwantformyspeakers,andsinceImnotgoodwithwoodworkingitwillbeeasiertofollowapremaidsetofinstructions.16

SimilarlyIwillbasetheothertwocabinetsoffoftheCM7Towercaseinstructions.17Iliketheideaofcreatingatallertowertoreachupandabovethebackofadeskwhileplacingthespeakersbehindthedesksincethisismostlikelywheremyspeakerswillendup.Iwanttobringtheheightupto4feetandkeepthewidthanddepthandgetridoftheportsinceitwillnotbeneededtoextendbass.

15LoudspeakersPg8916http://www.northcreekmusic.com/Thunder/ThunderInfo.htm17http://www.northcreekmusic.com/CM7/CM7TowerCabinet.PDF

Thompson WorksCitedNewell, Philip, and Keith Holland. Loudspeakers for Music Recording and Reproduction. Oxford: Focal

Press, 2007

Murphy, John L. Introduction to Loudspeaker Design. Andersonville: True Audio, 1998

Dickason, Vance. Loudspeaker Design Cookbook 7th Edition. Peterborough: Audio Amateur Press, 2006

Totem Acoustics. 2009. Totem. Totem Acoustics: Totem Acoustics. http://www.totemacoustic.com/ (accessed January 21, 2009)

Lyons, John. 2007. The Alamo Speaker Project. http://wiki.fa.mtu.edu/wiki/index.php/The_Alamo_Speaker_Project (accessed February 8th, 2009)

Dlugos, David. 2008. T-line Speakers. http://t-linespeakers.org/ (accessed February 8th, 2009)

Behringer. 2009. Behringer: DCX2496. http://www.behringer.com/EN/Products/DCX2496.aspx (accessed February 8th, 2009) NorthCreekMusicSystems.2006.CM7LoudspeakerSystem.http://www.northcreekmusic.com/CM7/CM7_Loudspeaker_System.htm.(accessedFebruary11,2009)NorthCreekMusicSystems.2006.ThunderSubwoofer.http://www.northcreekmusic.com/Thunder/ThunderInfo.htm.(accessedFebruary11,2009)HollywoodDJ.2009.AlesisRA150.http://hollywooddj.com/ra150.html.(accessedFebruary11,2009)GrabCart.2009.AlesisRA500.http://www.grabcart.com/product/ele/accessories/instrumentproalera500ale/AlesisRA500.(accessedFebruary11,2009)MadisoundSpeakerComponents.2009.MadisoundSpeakerComponents.Inc.http://www.madisound.com/catalog/index.php?cPath=45(accessedFebruary11,2009)SEAS.2008.SEASPrestigeP18RNX7PolyConeWoofer.http://www.madisound.com/pdf/seas/H1350.pdf(accessedFebruary11,2009)FountekElectronicsCompany.,Ltd.2008.FountekNeoCD3.0RibbonTweeter.http://www.madisound.com/catalog/PDF/neocd3.pdf(accessedFebruary11,2009)Peerless.2008.PeerlessXXLS12Subwoofer.http://www.madisound.com/catalog/product_info.php?cPath=45_338_381&products_id=1470.(accessedFebruary11,2009)Peerless.2008.PeerlessXLS12Subwoofer.http://www.madisound.com/catalog/PDF/peerless/830500.pdf.(accessedFebruary11,2009)Krutke,John.2008.Zaphaudio.http://zaphaudio.com/6.5test/.(accessedFebruary11,2009)SwansSpeakerSystems.2004.HiViRTC1AIsodynamicTweeter.http://www.madisound.com/catalog/PDF/hivi/rt1ca.pdf(accessedFebruary11,2009)